A variety of benign and malignant skin diseases are characterized histologically by the presence of prominent mononuclear cell infiltrates not only in the dermis but also in the epidermis. The mechanisms by which these benign or malignant lymphoid cells move from the blood into specific areas within the skin are poorly understood. The present studies are designed to clarify our understanding of these mechanisms. Available data has suggested several testable hypotheses, including the possibility that epidermal migration/invasion is a property characteristic of a discrete subpopulation of T cells with a special affinity for the skin in general and the epidermis in particular. Using the model of allergic contact dermatitis (ACD) reactions in mice, we are attempting to quantitate the capacities of variously purified subpopulations of radiolabeled normal and malignant mononuclear cells to be recruited into ACD reaction sites. Normal lymphoid cells will be fractionated into discrete subpopulations using standard immunological methods involving extensive use of monoclonal antibodies and immunoadsorbent plates. Studies will be undertaken to compare the migration/localization of antigen-specific versus nonspecific T cells:radiolabeled T cell subsets from DNFB and TNCB-immune mice will be injected into immune mice undergoing ACD reactions to either DNFB or TNCB. Methods to be utilized in enriching cells suspensions for antigen-specific cells will include in vitro restimulation with antigen as well as use of immunoadsorbent dishes coated with either antigen or anti-idiotypic antibodies. The migration into/within the skin of a number of sublines of various murine lymphomas will also be studied: these sublines are being established by serial passage in different organs including the skin. Additional studies will be directed at further characterization of the origin, phenotype, and function of a previously underscribed population of Thy-1+ intraepidermal dendritic cells: these studies involve bone marrow chimeras, further phenotypic characterization using immunofluorescence with antibodies directed against a variety of cell surface antigens, and the testing of Thy-1+-enriched suspensions (obtained by "panning") for immunocompetence in a variety of in vitro assays. Finally, we will continue to study the pathogenetic mechanisms involved in IgE-mediated contact hypersensitivity reactions: the role of the mouse basophil will be examined as will the immunologic phenotype of the cells responsible for successful adoptive transfer of these reactions.